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| United States Patent |
6,251,485
|
|
Harris
, et al.
|
June 26, 2001
|
Fast-setting latex coatings and formulations
Abstract
A fast-setting coating material can be prepared by contacting a stable
aqueous dispersion of a polymer that contains strong cationic groups and
weak acid groups onto a substrate that is basic or rendered to be basic.
Alternatively, the coating material can be prepared by contacting in
either order or concurrently the surface of a substrate with two separate
polymers, one of which contains strong cationic groups, and the other of
which contains weak acid groups. In this case, the substrate need not be
basic for the coating to quickly set.
| Inventors:
|
Harris; John K. (Midland, MI);
Schmidt; Donald L. (Midland, MI);
Rose; Gene D. (Midland, MI)
|
| Assignee:
|
The Dow Chemical Company (Midland, MI)
|
| Appl. No.:
|
421662 |
| Filed:
|
October 20, 1999 |
| Current U.S. Class: |
427/385.5; 427/407.1 |
| Intern'l Class: |
B05D 003/00 |
| Field of Search: |
427/407.1,385.5
|
References Cited
U.S. Patent Documents
| 3947396 | Mar., 1976 | Kangas et al. | 260/29.
|
| 4544697 | Oct., 1985 | Pickelman et al. | 524/458.
|
| 4544723 | Oct., 1985 | Upson et al. | 524/347.
|
| 4582663 | Apr., 1986 | Pickelmann et al. | 264/517.
|
| 4622360 | Nov., 1986 | Gomi et al. | 527/507.
|
| 4704324 | Nov., 1987 | Davis et al. | 428/308.
|
| 4859384 | Aug., 1989 | Fibiger et al. | 264/45.
|
| 4929666 | May., 1990 | Schmidt et al. | 524/516.
|
| 5310581 | May., 1994 | Schmidt et al. | 427/558.
|
| 5527853 | Jun., 1996 | Landy et al. | 524/521.
|
| Foreign Patent Documents |
| 000426 | Jan., 1979 | EP.
| |
Other References
Daniels, E. S., et al., Progress in Organic Coatings, vol. 19, pp. 359-378
(1991).
Kotz, J., et al., Acta Polymer, vol. 43, pp. 193-198 (1992).
Ooka, M., et al., Progress in Organic Coatings, vol. 23, pp. 325-338
(1994).
Padget, J. C., Journal of Coatings Technology, vol. 66, No. 839, pp. 89-105
(1994).
Shalbayeva, G. B., et al., Polymer Science U.S.S.R., vol. 26, No. 6, pp.
1421-1427 (1984).
|
Primary Examiner: Cameron; Erma
Attorney, Agent or Firm: Willis; Reid S.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This invention is a divisional of application U.S. Ser. No. 08/862,274
filed May 23, 1997, now U.S. Pat. No. 5997952.
Claims
What is claimed is:
1. A method of preparing a fast-setting coating on a substrate having a
surface comprising the steps of contacting the surface of the substrate
with a) a first stable aqueous dispersion containing a first polymer
having pendant strong cationic groups, and b) a second stable aqueous
dispersion of a second polymer having pendant weak acid groups; wherein
the contact of the polymers with the surface is made in any order or
concurrently, wherein the first and second polymer each have structural
units formed from the polymerization of a non-interfering polymerizable
monomer and wherein the pH of the first or the second stable aqueous
dispersion is at least about 5.
2. The method of claim 1 wherein the first polymer further has pendant weak
acid groups and the pH of the second stable aqueous dispersion is at least
about 5.
3. The method of claim 1 wherein the weak acid groups are structural units
formed from the polymerization of acrylic acid, methacrylic acid, itaconic
acid, .beta.-carboxyethyl acrylate, or vinylbenzoic acid, or a combination
thereof; and the strong cationic groups are structural units formed from
the polymerization of a trialkylaminmoniumalkyl acrylate; a
trialkylammoniumalkyl methacrylate, a trialkylammoniumalkyl acrylamide, a
dialkylsulfoniumn salt, a benzylsulfonium salt, a cyclic sulfonium salt, a
2-methacryloxyethyltri-C.sub.1 -C.sub.20 -alkyl-phosphonium salt, a
2-nethacryl-oxyethyltri-C.sub.1 -C.sub.20 -aralkyl-phosphonium salt, a
2-methacryl-oxyethyltri-C.sub.1 -C.sub.20 -aryl-phosphonium salt, a
tri-C.sub.1 -C.sub.18 -alkyl-vinylbenzylphosphonium salt, a tri-C.sub.1
-C.sub.18 -aralkyl-vinylbenzylphosphonium salt, a tri-C.sub.1 -C.sub.18
-aryl-vinylbenzylphosphonium salt, a C.sub.3 -C.sub.18 -alkenyltrialkyl-
phosphonium salt, a C.sub.3 -C.sub.18 -aralkyl-phosphonium salt, or a
C.sub.3 -C.sub.18 -aryl-phosphonium salt, or a combination thereof; and
the non-interfering polymerizable monomer is an acrylate, a methacrylate,
or a styrenic compound, or a combination thereof.
4. The method of claim 3 wherein the weak acid groups are structural units
formed from the polymerization of acrylic acid or methacrylic acid, or a
combination thereof; the strong cationic groups are structural units
formed from the polymerization of an ethylenically unsaturated quaternary
ammonium salt; and the non-interfering polymerizable monomer is methyl
methacrylate, butyl acrylate, 2-hydroxyethyl methacrylate,
4-methacryloxy-2-hydroxy-benzophenone, or
2-(2'-hydroxy-5-methacrylyloxyethylphenyl)-2H-benzotriazole, or a
combination thereof.
5. The method of claim 4 wherein the ethylenically unsaturated quaternary
ammonium salt is 2-trimethylammonium chloride, and the non-interfering
polymerizable monomer is methyl methacrylate or butyl acrylate or a
combination thereof.
6. The method of claim 1 wherein the substrate is cured Portland cement,
uncured Portland cement, aluminous cement, metal, glass, paper, plastic,
cloth, wood, or leather.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a stable aqueous dispersion that forms a
water-resistant fast-setting coating when applied to a suitable substrate.
Coating are generally used to provide a protective barrier for applications
such as floors, automobiles, exteriors and interiors of honses, as well as
painted roads. Protective coatings for floors, for example, have been
known since the mid 1950s. Many of the early coating materials were
applied using petroleum- or naphthene-based solvents, and as such were
undesirable due to the toxicity and flammability of these solvents.
Water-based synthetic emulsion compositions such as styrene resin
emulsions, styrene-acrylate copolymer resin emulsions, and acrylate
emulsions, developed in the early 1960s, gradually replaced organic
solvent-based compositions. Although the water-based compositions are
preferable to organic solvent-based compositions for safety and
environmental reasons, coatings prepared from water-based compositions
require long drying times. During drying, the coatings are susceptible to
a number of events that may produce a defective coating, such as drips,
sags and runs. Moreover, until the coating is set, it is vulnerable to
contamination by dust or water contact, which may also lead to a marred
coating. These effects can be minimized by the use of volatile cosolvents
which accelerate the drying process, but the cosolvents reintroduce
environmental problems that the water-based systems were designed to
address.
In addition to the environmental concerns, one of the challenges that
remains is to develop latexes that coalesce at room temperature, without
leaving a tacky surface.
In view of the deficiencies in the art, it would be desirable to provide a
coating that rapidly becomes resistant to marring, defects, and
contamination during drying, using a stable aqueous dispersion that does
not require environmentally unacceptable cosolvents or crosslinking
curatives.
SUMMARY OF THE INVENTION
The present invention addresses a need in the art by providing a way to
prepare coatings that set quickly upon contact with a substrate.
Accordingly, in one aspect, the present invention is a coated material
comprising a substrate having a surface and a coating thereupon, wherein
the coating is prepared by any of the steps of:
a) contacting the surface of the substrate with a stable aqueous dispersion
that contains a polymer having pendant strong cationic groups and pendant
weak acid groups; or
b) contacting the surface of the substrate with a stable aqueous dispersion
containing a first polymer having pendant strong cationic groups, and a
stable aqueous dispersion of a second polymer having pendant weak acid
groups, the contact of the polymers with the surface being made in any
order or concurrently;
with the proviso that when the coating is prepared by the method of (a),
the surface of the substrate is, or is treated to be, sufficiently basic
so that the stable aqueous dispersion sets in less time than the time
required for a latex that only has pendant strong cation groups or pendant
weak acid groups to set.
In a second aspect, the present invention is a method of preparing a
fast-setting coating on a substrate having a surface comprising either of
the steps of:
a) contacting the surface of a substrate with a stable aqueous dispersion
that contains a polymer having pendant strong cationic groups, and pendant
weak acid groups; or
b) contacting the surface of the substrate with a stable aqueous dispersion
that contains a first polymer having strong cationic groups, and a stable
aqueous dispersion that contains a second polymer having weak acid groups,
the contact of the polymers with the surface being made in any order or
concurrently; with the proviso that when the fast-setting coating is
prepared by the method of (a), the surface of the substrate is, or is
treated to be, sufficiently basic so that the stable aqueous dispersion
sets in less time than the time required for a latex that only contains
pendant strong cation groups or pendant weak acid groups to set.
In a third aspect, the present invention is a stable aqueous dispersion
comprising a polymer having strong cationic groups, weak acid groups, and
structural units formed from the polymerization of a non-interfering
monomer, wherein the ratio of structural units formed from the
polymerization of the non-interfering polymerizable monomer to strong
cationic groups and the weak acid groups is from about 70:30 to about
99:1, with the proviso that the strong cationic groups are associated with
non-alkaline counterions.
DETAILED DESCRIPTION OF THE INVENTION
The fast-setting coated material of the present invention can be prepared
by contacting a substrate with a stable aqueous dispersion that contains a
polymer having structural units formed from the polymerization of: a) a
polymerizable strong cationic monomer, and b) a polymerizable weak acid
monomer. In this aspect of the present invention, the substrate is, or is
treated to be, sufficiently basic that the stable aqueous dispersion sets
in a time that is less than the time required for a latex that only
contains pendant strong cation groups or pendant weak acid groups to set.
The term "sufficiently basic" refers to sufficiency of amount of base as
well as base strength. A coating "sets" or is "dry-to-the-touch" when it
has formed a skin with sufficient mechanical integrity such that no
portion of the skin is removed when it is touched lightly with a finger,
and no portion is washed off the substrate when rinsed under a light
stream of water.
As used herein, the term "polymerizable strong cationic monomer" refers to
a monomer that contains ethylenic unsaturation and a cationic group having
a charge that is independent of pH. Similarly, the term "polymenizable
weak acid monomer" refers to a monomer that contains ethylenic
unsaturation and an acid group having a pK.sub.a in the range of about 2
to about 10. The term "structural units formed from the polymerization of
. . ." is illustrated by the following example:
##STR1##
In addition to structural units formed from the polymerization of a
polymerizable strong cationic monomer and a polymerizable weak acid
monomer, the polymer also preferably includes structural units formed from
the polymerization of a polymerizable non-interfering monomer. The term
"polymerizable non-interfering monomer" is used herein to refer to a
monomer that does not adversely affect the fast-setting nature of a
coating prepared from the stable aqueous dispersion of the polymer.
Polymerizable weak acid monomers that are suitable for the preparation of
stable aqueous dispersion used to prepare the water-resistant fast-setting
coating include ethylenically unsaturated compounds having carboxylic
acid, phenolic, thiophenolic, or phosphinyl functionality. Preferred
polymerizable weak acid monomers include acrylic acid, methacrvlic acid,
itaconic acid, .beta.-carboxyethyl acrylate (usually as a mixture of
acrylic acid oligomers), vinylbenzoic acid, and 2-propenoic acid:
2-methyl-, (hydroxyphosphinyl) methyl ester. Acrylic acid and methacrylic
acid are more preferred weak acid monomers.
The polymerizable strong cationic monomer is associated with a non-alkaline
counterion, which may be, for example, halide such as chloride, bromide,
or iodide, as well as nitrate or sulfate. As used herein, the term
"non-alkaline counterion" refers to a counterion that does not cause
sufficient ionization of the weak acid to render the stable aqueous
dispersion unstable. Thus, a bicarbonate counterion would not be
appropriate if a carboxylic acid were the weak acid, since this counterion
would, in sufficient quantity, raise the pH of the stable aqueous
dispersion to an unstable level. For example, for a stable aqueous
dispersion containing 2.3 mole percent each of a quaternary ammonium salt
and a carboxylic acid, the presence of a sufficient amount of a
bicarbonate counterion to raise the pH of the latex to above 5.5 would
cause the dispersion to become unstable.
Suitable polymerizable strono cationic monomers include salts of
ethylenically unsaturated compounds having quaternary ammonium, sulfonium,
cyclic sulfoniumn and phosphonium functionality. Examples of suitable
monomers having quaternary ammonium functionality include ethylenically
unsaturated trialkylammonium salts such as vinylbenzyl tri-C.sub.1
-C.sub.4 -alkylammonium chloride or bromide; trialkylammoniumalkyl
acrylates or methacrylates such as
2-[(methacryloyioxy)ethyl]-trimethylammonium chloride and
N,N-diethyl-N-methyl-2-[(1-oxo-2-propenyl)oxy] ethanaminium methyl sulfate
(Chem. Abstracts Reg. No. 45076-54-8); and trialkylammoniumalkyl
acrylamides such as
N,N,N-trimethyl-3-[(2-methyl-1-oxo-2-propenyl)amino]-1-propanaminium
chloride (Chem. Abstracts Reg. No. 51441-64-6) and
N,N-dimethyl-N-[3-[(2-methyl-1-oxo-2-propenyl)amino]propyl]-benzenemethami
nium chloride (Chem. Abstracts Reg. No. 122988-32-3). A preferred
polymerizable quaternary ammonium salt is
2-[(methacryloyloxy)ethyl]trimethylammonium chloride.
Examples of polymerizable unsaturated sulfonium salts include
dialkylsulfonium salts such as
[4-ethoxy-3-(ethoxycarbonyl)-2-methylene-4-oxobutyl]dimethylsulfonium
bromide (Chem. Abstracts Reg. No. 63810-34-4); and vinylbenzyl
dialkylsulfonium salts such as vinylbenzyl dimethylsulfonium chloride.
Examples of polymerizable cyclic sulfonium salts include
1-[4-[(ethenylphenyl)methoxy]phenyl]tetrahydro-2H-thiopyranium chloride
(Chem. Abstracts Reg. No. 93926-67-1): and vinylbenzyl
tetrahydrothio-phenonium chloride, which can be prepared by the reaction
of vinylbenzyl chloride with tetrahydrothiophene.
Examples of polymerizable phosphonium salts include
2-methacryloxyethyltri-C.sub.1 -C.sub.20 -alkyl-, aralkyl-, or
aryl-phosphonium salts such as
2-methacryloxyethyltri-n-octadecylphosphonium halide (Chem. Abstracts Reg.
No. 166740-88-1); tri-C.sub.1 -C.sub.18 -alkyl-, aralkyl-, or
aryl-vinylbenzylphosphonium salts such as
trioctyl-3-vinylbenzylphosphonium chloride,
trioctyl-4-vinylbenzylphosphonium chloride (Chem. Abstracts Reg. No.
15138-12-4), tributyl-3-vinylbenzylphosphonium chloride,
tributyl-4-vinylbenzylphosphonium chloride (Chem. Abstracts Reg. No.
149186-03-8), triphenyl-3-vinylbenzylphosphonium chloride, and
triphenyl-4-vinylbenzylphosphonium chloride (Chem. Abstracts Reg. No.
145425-78-1); C.sub.3 -C.sub.18 -alkenyltrialkyl-, aralkyi-, or
aryl-phosphonium salts such as 7-octenyltriphenylphosphonium bromide
(Chem. Abstracts Reg. No. 82667-45-6): and
tris(hydroxymethyl)(1-hydroxy-2-propenyl)phosphonium salts (Chem.
Abstracts Reg. No. 73082-48-1).
An example of a polymerizable monomer that contains both a weak acid group
and a strong cationic group is
N-(4-carboxy)benzyl-N,N-dimethyl-2-[(2-methyl-1-oxo-2-propenyl)-oxy]
ethanaminium chloride.
It is possible to add strong cationic functionality to an already prepared
polymer. For example, a polymerizable monomer having a weak acid group can
be copolymerized with a polymerizable non-interfering monomer containing
an electrophilic group, such as a vinylbenzyl halide or a glycidyl
methacrylate, to form a polymer having a weak acid group and an
electrophilic group. This polymer can then be post-reacted with a
nucleophile such as a tertiary amine or a dialkyl sulfide, which can
displace the halide group or oxirane groups and form a benzylonium salt as
illustrated:
##STR2##
where A is a pendant weak acid group; Ar is an aromatic group, preferably a
phenyl group; L is a leaving group, preferably a halide group, more
preferably a chloride group; and Nu is preferably a dialkyl sulfide such
as dimethyl sulfide and diethyl sulfide, a cyclic sulfide such as
tetrahydrothiophene: or a tertiary amine such as trimethyl amine, triethyl
amine, tripropyl amine, tributyl amine, and triethanol amine.
In another example of adding strong cationic functionality to an already
prepared polymer, a polymer backbone that contains pendant acid groups and
a tertiary amine or a sulfide can be post-reacted with a suitable
alkylating reagent such as an alkyl halide to form a polymer that contains
acid groups and strong cationic groups:
##STR3##
where RL is an alkylating reagent.
Examples of non-interfering polymerizable monomers include acrylates such
as methvl acrylate, ethyl acrylate, butyl acrylate, 2-hydroxyethyl
acrylate, 2-hydroxypropyl acrylate, glycidyl acrylate, and allyl acrylate,
methacrylates such as methyl methacrylate, ethyl methacrylate, butvl
methacrylate, allyl methacrylate, glycidyl methacrylate, 2-hydroxyethyl
methacrylate, and 2-hydroxypropyl methacrylate; alkenyl aromatic
hydrocarbons such as 4-methacryloxy-2-hydroxy-benzophenone,
2-(2'-hydroxy-5-methacrylyloxyethylphenyl)-2H-benzotriazole; and C.sub.1
-C.sub.4 alkyl- or alkenyl-substituted styrenes, preferably styrene,
.alpha.-methylstyrene, vinyltoluene, and vinylbenzyl chloride. Other
examples of non-interfering species include C.sub.3 -C.sub.18
-perfluoroalkyl methacrylates such as 2-(perfluorooctyl)ethyl
methacrylate; C.sub.3 -C.sub.18 -perfluoroalkyl acrylates such as
2-[ethyl[(heptadecafluorooctyl)-sulfonyl]amino]ethyl 2-propenoate; and
C.sub.3 -C.sub.18 -perfluoro-alkyl vinylbenzenes. (See U.S. Pat. No.
4.929,666, column 4, lines 54 to 68, and column 5, lines 1 to 30.)
The ratio of the pendant weak acid groups to the pendant strong cationic
groups is application dependent, but is generally in the range of about
4:1 to about 1:4. The ratio of the structural units formed from the
polymerization of the polymerizable non-interfering monomer to the weak
acid groups and the strong cationic groups varies depending on the percent
solids of the stable aqueous dispersion, but is preferably not less than
70:30, more preferably not less than 80:20, more preferably not less than
90:10, and most preferably not less than 94:6; and preferably not greater
than 99.5:0.5, more preferably not greater than 99: 1, and most preferably
not greater than about 98:2.
In general, the higher the solids content, the lower the concentration of
the total ionic species that is required to form the quick-set coatings.
The solids content of the stable aqueous dispersion is application
dependent, but preferably not less than 10, more preferably not less than
20, and most preferably not less than 30 weight percent, and preferably
not more than 60, more preferably not more than 55, and most preferably
not more than 50 weight percent.
The stable aqueous dispersion can be prepared by any suitable means, and is
advantageously prepared by the steps of: 1) preparing a seed latex; 2)
diluting the seed latex with water; 3) contacting the diluted solution
with a radical initiator, a polymerizable non-interfering monomer, a
polymerizable weak acid monomer, and a strong cationic monomer; and 4)
polymerizing the solution from step 3 under such conditions to form a
stable aqueous dispersion having non-interfering groups, pendant strong
cationic groups, and pendant weak acid groups.
The seed latex is preferably prepared by emulsion polymerization in a batch
process using a cationic surfactant. The seed latex acts as a locus of
polymerization for subsequent monomer addition, so that the formation of
new particles is minimized and greater uniformity in the distribution of
particle size in the final product is achieved. Thus, the monomer or
monomers used to prepare the seed latex are chosen to form particles that
have an affinity for the monomers subsequently added, so that
polymerization occurs preferentially in or on the seed latex particles.
The extent to which the seed latex is diluted in step 2 is a function of
the desired particle size and the percent solids in the final latex, and
can be readily determined by one of ordinary skill in the art.
It is also possible to prepare a stable aqueous dispersion from a preformed
polymer. The preformed polymer can be dissolved in a suitable solvent,
then dispersed in water by any suitable method. The solvent can then be
removed and the solids content adjusted to form a so-called artificial
latex.
The stable aqueous dispersion may optionally contain fillers, pigments,
dyes, fungicides, bateriacides, thickeners, coalescing aids, and
defoamers, that do not cause premature coagulation of the dispersion.
Fillers may include clays, silica, ceramics, and other stable aqueous
dispersions.
A fast-setting coated material can be prepared when the stable aqueous
dispersion that contains the polymer hatting the strong cationic groups,
the weak acid groups, and 5 optionally, structural units formed from the
polymerization of the polymerizable non-interfering monomer, is contacted
with a substrate having a contact surface which is, or is treated to be,
sufficiently basic so that the stable aqueous dispersion sets in less than
the time required for a latex that only contains pendant strong cation
groups or pendant weak acid groups (but not both) to set, preferably
within 5 minutes, and more preferably within 3 minutes, and most
preferably within 1 minute. The basicity of the substrate required to
cause the dispersion to set rapidly depends on the pK.sub.a of the weak
acid groups on the polymer. The lower the pK.sub.a of the weak acid, the
weaker the base required to cause rapid setting. The stronger the base and
the higher the concentration of the base, the faster the setting.
Though not bound by theory, it is believed that the rapid dry-to-the-touch
coating is formed by a coacervation process. In this process, the basic
substrate acts as a proton sink by extracting protons from the weak acid
groups to form the conjugate base, which can then bind irreversibly and
rapidly with the strong cationic group to form an irreversible
crosslinking network. This crosslinked network is believed to represent
the coating after it has set.
##STR4##
In the above illustration, B.sup.- is a basic moiety that is associated
with the substrate. BH, the conjugate acid of B.sup.-, preferably has a
higher pK.sub.a than the weak acid (which is a carboxylic acid group in
the illustration). However, this need not be the case. For example, if
there is a sufficient amount of B.sup.- present on the substrate, the
conjugate acid BH may actually have a pK.sub.a that is the same as, or
lower than, the pK.sub.a of the weak acid. presumably because once the
proton is abstracted by B.sup.-, the process is irreversible.
An indication of the surface basicity may be provided, for example, by
contacting the surface of the substrate with water-wetted pH paper. The pH
necessary to induce coacervation will be depend on the pK.sub.a of the
weak acid; for a polymer containing pendant carboxylic acid units, for
example, the pH of the water in contact with the substrate is not less
than 6, more preferably not less than 8, and most preferably not less than
10.
The substrate may be inherently basic. Such substrates include cementations
materials such as Portland cement, aluminous cement, inorganic mortar, or
cementatious fiber board. The substrate, if not inherently basic, may be
treated to be sufficiently basic to cause the coated material to quickly
set. For example, the surface of the substrate may be treated with an
aqueous solution having a pH that is greater than the pK.sub.a of the weak
acid, prior to, or concurrent with, the application of the stable aqueous
dispersion of the polymer to the surface of the substrate. Such basic
aqueous solutions include, but are not restricted to, alkali metal and
alkaline earth metal phosphates, carbonates, bicarbonates, and hydroxides.
Preferred substrates that can be treated with base include metal, glass,
paper, plastic, cloth, wood, and leather. The substrate may also take a
specific shape such as the shape of a hand, for the purposes of forming a
latex glove.
The substrate may also include a filler material that renders the surface
of the substrate sufficiently basic to cause the stable aqueous dispersion
of the polymer to form a fast-setting coating. Lime and calcium carbonate
are examples of such filler materials.
In another embodiment of the present invention, fast-setting coatings can
be prepared by contacting a substrate with a first stable aqueous
dispersion that contains a polymer having structural units formed from the
polymerization of a polymerizable strong cationic monomer; and a second
stable aqueous dispersion that contains a polymer having structural units
formed from the polymerization of a weak acid monomer, wherein the pH of
the first or the second stable aqueous dispersion, or both the first and
the second stable aqueous dispersion, is at least about 5. The stable
aqueous dispersions may be contacted with the substrate in any order or
substantially concurrently, preferably substantially concurrently, and
surprisingly, the substrate need not be basic or rendered basic. The
second stable aqueous dispersion is preferably stabilized in the presence
of an anionic surfactant such as a sulfate, including sodium lauryl
sulfate, or DOWFAX EB.TM. surfactant (obtained by The Dow Chemical
Company). The sulfate may also be present as end-groups on the polymer
chains resulting from the use of persulfate initiator during the
polymerization of the anionic latex. The first and second stable aqueous
dispersions are preferably applied to the substrate using a plural
component sprayer.
Both the first and the second stable aqueous dispersions preferably have
structural units formed from the polymerization of the polymerizable
non-interfering monomer. The mole percent of structural units formed from
the polymerization of the strong cationic monomer in the first stable
aqueous dispersion of the polymer is preferably not less than 0.5, more
preferably not less than 1, and most preferably not less than 2 mole
percent, and preferably not greater than about 20, more preferably not
greater than 10, and most referably not greater than 5 mole percent, based
on the total mole percent of strong cationic monomer and non-interfering
monomer. The mole percent of structural units formed from the
polymerization of the weak acid monomer in the second stable aqueous
dispersion of the polymer is also preferably not less than 0.5, more
preferably not less than 1, and most preferably not less than 2 mole
percent, and preferably not greater than about 20, more preferably not
areater than 10, and most preferably not greater than 5 mole percent,
based on the total mole percent of strong cationic monomer and
non-interfering monomer.
The coated materials of the present invention have wide applicability,
including painted concrete roads, where a fast-setting coating can be
prepared in the absence of solvents or crosslinking curatives, by merely
applying the stable aqueous dispersion of the polymer (or polymers) to the
surface of the road. Other uses include primers for stucco houses or
cementatious fiber boards. The aqueous dispersions can also be used to
coat cured or uncured cement to reduce water evaporation, thereby
improving the physical properties of the final concrete. The dispersions
can also be used to prepare latex gloves or condoms by dipping a basic
form or mold into the stable aqueous dispersion to cause rapid setting of
the dispersion on the form.
In the most preferred formulations, the stable aqueous dispersions used to
prepared the coated materials have a shelf-stability of at least 6 months,
preferably at least one year. The formulations may also contain additives
such as pigments, dyes, fungicides, and bacteriacides.
The following examples are for illustrative purposes only and are not
intended to limit the scope of this invention.
EXAMPLE 1
Preparation of a Fast-Setting Clear Coating
The stable aqueous dispersion was prepared in a two-step process. First, a
cationic surfactant stabilized polystyrene seed latex prepared using a
batch process. Next, a portion of the seed latex is used in a continuous
addition process to prepare a second, film-forming latex containing a
carboxylic acid and a quaternary ammonium functional monomer.
The cationic latex seed was prepared in the following manner. To a 1-liter,
3-neck, glass reaction flask equipped with a nitrogen inlet, a reflux
condenser with a nitrogen outlet, and a mechanical stirrer was added
styrene (100 g). ARQUAD.TM. 18-50 octadecyltrimethlammonium chloride
surfactant (a trademark of AkzoNobel, 20 g active), hydrogen peroxide (3.3
g. 1.0 g active) water (200 g) and iron sulfate solution (0.25 g in 100 g
water). The flask was heated to 70.degree. C. over 2 hours with stirring
under nitrogen, after which the stirring was stopped and the heating
source removed. The latex seed was allowed to sit overnight in the flask.
The result was an opaque, high viscosity dispersion with 35.8 percent
solids. The particle size was 407 .ANG. (mean value) and 393 .ANG. (median
value).
The film-forrning latex was prepared from the cationic seed latex using a
continuous addition polymerization method. Syringe pumps were used as the
continuous addition control means. To a 2-liter, 3-neck. glass reaction
flask equipped with a nitrogen inlet, a reflux condenser with a nitrogen
outlet, and a mechanical stirrer was added water (452.3 g) and the
cationic seed latex (8.8 g). The flask was heated to 60.degree. C. and
stirred. Table 1 shows the solutions that were prepared for continuous
addition.
TABLE 1
Stream Component Amount
1 Butyl Acrylate 176 g
Methyl Methacrylate 124 g
Methacrylic Acid 5.3 g
2 M-Quat.sup.a 17.3 g (12.8 g active)
3 t-Butylhydroperoxide 1.8 g (1.3 g active)
4 Sodium Formaldehyde Sulfoxylate 0.96 g in 10 ml water
.sup.a 2-[(methacryloyloxy)ethyl] trimethylammonium chloride obtained as a
74 percent aqueous solution from Bimax Inc., 717 Chesapeake Ave.,
Baltimore, MD 21225
The components from the four streams were added over the first four hours
of polymerization. After completion of addition, polymerization was
continued at 60.degree. C. for 0.5 hour. The resulting latex was filtered
and found to have a solids content of 37.0 percent. Table 2 shows the
composition of the latex.
TABLE 2
Molecular weight
Monomer Weight percent Mole percent g/mol
Butyl Acrylate 55.3 50.2 128.1
Methyl Methacrylate 39.0 45.3 100.1
Methacrylic Acid 1.7 2.3 86.1
M-Quat 4.0 2.3 207.7
The particle size was 1550 .ANG. (mean) and 1450 .ANG. (median).
A clear, fast-setting coating was prepared by applying a coat of the latex
to a cementatious fiber board using a paint brush. The sample was observed
at 22.4.degree. C. and 65 percent relative humidity. Thirty seconds after
application of the latex, the coated, cementations fiber board was placed
under running water. The coating showed no signs of bleeding, running or
any detrimental effects. Within twenty minutes of application the latex
dried to a clear film.
EXAMPLE 2
Preparation of a Fast-Setting Pigmented Coating
A titanium dioxide pigment slurry is used to prepare a pigmented latex
coating to demonstrate that a fast-setting coating can be obtained on an
alkaline surface using pigmented coating formulations. The composition of
the titanium dioxide pigment slurry is given in Table 3.
TABLE 3
Amount
Component (weight percent)
Water 31.0
Ti-Pure .TM. R-900 Titanium Dioxide.sup.a 66.5
RHODAQUAT .TM. M242C/26 Cationic Surfactant.sup.b 2.20
FOAMASTER .TM. V Nonionic Surfactant.sup.c 0.30
.sup.a (a trademark of E. I. du Pont de Nemours and Company)
.sup.b (a trademark of Rhone-Poulenc)
.sup.c (a trademark of Henkel)
The titanium dioxide pigment slurry was prepared bv mixing the titanium
dioxide into the water containing the surfactants under high speed
shearing to form a smooth, viscous dispersion. To a glass jar was added
29.4 g of this slurry. then 5.5 g of deionized water. The diluted slurry
was mixed to form a uniform suspension. The latex having the composition
shown in Table 2 and a total solids content of 37.4 wt % was then mixed
with the slurry at about 350 rpm for 3 minutes. The resulting dispersion
had the consistency and color of whole milk. A coating of this dispersion
was applied with a paint brush onto a cementatious fiber board. After 1
minute the coating on the board was placed under a stream of running
water. There was no indication of pigment loss or any detrimental effect
to the coating. About 10 mL of the pigmented latex was transferred to a
spray bottle pressurized with nitrogen to about 30 psig. A small amount of
the pigmented latex was spayed onto a cementations fiber board. A uniform
coating of the cementations fiber board was obtained. Again, after about 1
minute, the coated board was placed under a stream of running water. There
was no indication of pigment loss or any detrimental effect on the
coating.
EXAMPLE 3
Forming a Fast-Setting Coating on Base-Treated Filter Paper
A 9.0-cm circle of Whatman #1 qualitative filter paper was cut into a 5.7
cm.times.7.0 cm rectangle, then taped to a glass plate along all edges.
The paper was soaked with saturated sodium bicarbonate solution, then
blotted with paper towels to remove excess fluid. A coating of latex
having a composition described in Table 2 was then spread on the coated
paper. Rapid setting of the latex film on the paper was apparent in less
than 15 seconds. After about 2 minutes the coating was completely
dry-to-the-touch. After 3 minutes, a drop of water w as place onto the
coated paper and beaded with no visible signs of bleeding. This drop test
was repeated several times with the same results.
EXAMPLE 4
Forming a Fast-Setting Coating on Base-Treated Newspaper
An 11-inch.times.17-inch (28-cm.times.43-cm) sheet of paper was suspended
in a hood and lightly sprayed with a 1.0 percent solids sodium bicarbonate
solution, then allowed to dry overnight. The following day, the sample was
coated with a thin layer of the latex having a composition described in
Table 2. The coating set in less than 10 seconds, it displayed no
indications of bleeding into the paper, and it produced a glossy surface.
EXAMPLE 5
Forming a Fast-Setting Coating on Base-Treated Cloth
A swatch of common clothing material (60% cotton, 40% polyester) was dipped
into a 1.0 percent by weight solution of sodium bicarbonate and allowed to
soak for 5 minutes. The swatch was then removed, squeezed as dry as
possible and taped to a glass plate. An 8-mil drawdown bar was then used
to spread across the swatch a sample of the latex having a composition
described in Table 2. The latex was dry-to-the-touch within 10 seconds.
Within 2 minutes, the excess water could be squeezed from the coated
material using a high-pressure laminated plastic roller. Within 30 minutes
the latex dried to a clear flexible coating with some level of gloss.
EXAMPLE 6
Plural Component Spraying with Alkaline Material
A Binks Mach 1 PCX Plural Component paint sprayer was used to apply a
blended stream of a latex having a composition described in Table 2, and a
3.0 percent by weight solution of K.sub.2 HPO.sub.4 to a sample of
oak-laminated plywood. The atomizing pressure was set at about 72 psig and
both storage vessels were set at approximately 35 psig. The coating became
dry-to-the-touch rapidly (less than 30 seconds). Two aluminum coupons
(Q-panel, Inc.) were also coated with similar results. The atomizing
pressure was decreased to 45 psig and the storage vessels pressured
dropped to 10 psig. The procedure was then repeated. The rate at which the
coating became dry-to-the-touch was unaffected, but the surface of the
coating was improved. A "Cold Rolled Steel" coupon (Q-panel) was also
coated easily using the same operating conditions and obtaining similar
results.
EXAMPLE 7
Plural Component Spraying Using an Anionic Latex
The paint sprayer described in Example 6 was used to apply a blended stream
of a latex having a composition described in Table 2, and an anionic latex
having a composition described in Table 4.
TABLE 4
Monomer Weight Percent Mole Percent
Butyl Acrylate 50.5 43.9
Methyl Methacrylate 43.0 47.9
Methacrylic Acid 5.95 7.7
Allyl Methacrylate 0.52 0.46
The atomizing pressure was set to 40 psig and the storage vessel pressure
was set to 7.5 psig. The spray was applied to a glass plate and the
resultant coating set in less than 30 seconds.
EXAMPLE 8
Plural Component Spraying with an Anionic Material
The paint sprayer described in Example 6 was used to apply a blended stream
of latex, having a composition described in Table 2, and an aqueous
anionic corrosion inhibiting solution, consisting of 4.45% by weight of
MIRANOL CS.RTM. (manufactured by Rhone Poulenc). The atomizing pressure
was set at 35 psig and the storage vessel pressure was set at 5 psig. The
coating was applied to an untreated aluminum coupon, a pre-treated
aluminum coupon (Q-panel, Inc.) and a pre-coated sample of PTO. The spray
formed an acceptable coating and set in less than 30 seconds on all three
test panels.
EXAMPLE 9
Plural Component Spraying with Cationic Latex and Anionic Latex
The paint sprayer described in Example 6 was used to apply a blended stream
of cationic latex, having a composition described in Table 5, and an
anionic latex, having a composition as described in Table 4. The atomizing
pressure was set at 35 psig and the storage vessel pressures were set at
10 psig. The coating was applied to an untreated glass plate. The spray
formed an acceptable coating and coacervated in less than 20 seconds. It
set in less than 30 seconds. The plate was placed under running water
after 1 minute with no detrimental effect to the coating. Two aluminum
coupons, one of which was pre-treated with phosphate (Q-panel, Inc.), were
also coated. The spray formed an acceptable coating and coacervated in
less than 15 seconds en both test panels.
TABLE 5
Monomer Weight Percent Mole Percent
Butyl Acrylate 56.2 51.3
Methyl Methacrylate 39.7 46.5
M-Quat 4.1 2.3
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